1. Field of the Invention
This invention relates generally to packing wells and more particularly to method of determining combination of critical parameters including the proppant density, proppant concentration, proppant to liquid mix ratio, screen size, pump rate, and circulating pressure, which will efficiently and effectively place the light weight proppants over an extended segment of a highly deviated or horizontal well, and then utilizing the selected parameters to pack the proppants in the well.
2. Description of the Related Art
Various techniques for open hole gravel packing of oil and gas wells are well known. Highly deviated and horizontal wells have become more common over the past few years. Wells which include several thousand feet of horizontal section, some times greater than 6,000 feet, have been drilled more recently and many such wells are expected to be drilled in the future. Wells with such long highly deviated or horizontal segments are referred to herein as the xe2x80x9cextended reach horizontal wells.xe2x80x9d Gravel or sand, which is relatively heavy (specific gravity of 2.65) compared to the carrying fluid (usually salt water) cannot be used effectively for packing several thousand feet of a continuous section of annulus between the well and the screen. Lighter proppants, which may be made from a variety of synthetic materials, have been used in packing the annulus of highly deviated wells. Extended reach open hole wells pose particular problems due to excessive friction forces over the length of such long horizontal sections. The aim is to completely (100 percent) pack the annulus over the entire length of the screen, which, as noted above, may be as much as 6,000 feet or more.
A horizontal open hole gravel pack is accomplished by circulating gravel slurry into the well while keeping circulating pressures below the fracture pressure. At the start of the gravel pack, gravel is deposited around the screen along the bottom of the hole building to some height at which point the velocity is sufficient to wash it down the hole. This process is called the Alpha wave. When the gravel or Alpha wave reaches the bottom of the hole, gravel is then deposited on top of the Alpha wave and the wellbore is back filled. This is called the Beta wave. There is a minimum circulating rate below which it is not possible to transport the gravel or Alpha wave completely to the end of the well.
It is not always possible to efficiently or effectively gravel pack a horizontal open hole well with standard gravel having a specific gravity of 2.65. But for a given Alpha wave height, a lower density gravel can be pumped at a lower rate. It now becomes possible to one hundred percent (100%) gravel pack a well which would not have been possible with a 2.65 specific gravity gravel. The low weight gravel can be transported at lower rates, which reduces the circulating pressure and keeps it below the fracture pressure.
A screen is placed along the length of the horizontal section of the well to be packed. A mixture of the proppant and a liquid (generally sea water) is pumped into the annulus between the screen and the well. The screen acts as a strainer to deposit the proppant in the annulus and allows the clean fluid to return to the surface via a wash pipe that extends from the well bottom to the surface.
Because of the extended annulus length to be packed, it is critical to determine the various parameters that interact with each other for efficient and effective packing of the annulus. Such parameters include the density of the proppant, proppant concentration, fluid/proppant mixture (xe2x80x9cslurryxe2x80x9d), pump rate, screen size, washpipe size, hydrostatic pressure, and the fracture pressure of the formation. The inventors of this application have determined through experiments and simulation values of the combination of the critical parameters that will efficiently transport the proppant to the entire extended reach of the annulus and effectively pack such annulus. This invention further provides a completion string that will allow complete packing of the annulus even when a segment of the wellbore collapses during the packing process.
The present invention provides a method for efficiently packing proppant in open hole annulus. The method provides at least one combination of a plurality of parameters which will provide an efficient and safe packing operation for extended reach horizontal open holes. For a given set of fixed parameters, such as the wellbore size and screen size, fracture pressure, include the proppant density, proppant and liquid mix ratio and pump rate. The wellbore size and the screen size are initially input into a simulation program which provides a combination of parameters that may include the total pack time for the Alpha wave (forward fill) and the Beta wave (back fill), the proppant density, proppant size, proppant and liquid mix ratio, the circulating pressure profile during packing operation. The packing operation is performed using the parameters that will provide the most efficient and effective packing operation.
Examples of the more important features of the invention thus have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto.